JPH08200865A - Cryogenic refrigerator - Google Patents

Abstract

(57) [Summary] [Purpose] A switching valve for selectively communicating the expansion space of the expander with the discharge side and the suction side of the compressor is operated quickly and smoothly. [Structure] The first pressure chamber 63c of the switching valve 63 is connected to the valve motor 54, the second pressure chamber is connected to the expansion space 5 of the expander 2, and the switching valve 63 is connected by the differential pressure between high pressure and low pressure.
The valve element 63b is operated.

Description

Detailed Description of the Invention

[0001]

This invention relates to a cryogenic refrigerator,
More specifically, the present invention relates to a cryogenic refrigerator in which a displacer is reciprocated by gas pressure in a cylinder of an expander, and adiabatic expansion of a refrigerant gas accompanying the reciprocating motion of the displacer generates cryogenic refrigeration. .

[0002]

2. Description of the Related Art Conventionally, a gas pressure drive type GM refrigerator having a GM (Gifford McMahon) cycle refrigeration cycle has been known as a cryogenic refrigerator of this type. The expander of this refrigerator comprises a cylinder, and a displacer and a slack piston that are reciprocally arranged in the cylinder. The displacer defines an expansion chamber at the tip of the cylinder. Through the regenerator of the above to communicate with the space on the base end side of the cylinder. The slack piston is arranged on the base end side of the cylinder so as to divide the base end side space into a gas supply / discharge chamber and an intermediate pressure chamber, and is engaged with the displacer at a predetermined stroke interval. The intermediate pressure chamber communicates with the surge volume, while the gas supply / discharge chamber communicates with a high pressure gas inlet and a low pressure gas outlet connected to the discharge side and the suction side of the compressor, respectively. Then, by periodically switching the supply / discharge of the refrigerant gas to / from the gas supply / discharge chamber or the expansion chamber, the slack piston is moved by the pressure difference between the gas supply / discharge chamber and the intermediate pressure chamber to reciprocate the displacer. The refrigerant gas expands in the expansion chamber due to the reciprocal movement of the cylinder, causing cold to be generated in the cylinder around the expansion chamber.

When switching the supply and discharge of the gas, it is roughly classified into one using an electric actuator such as a motor and a solenoid valve, and the gas pressure in the expander as disclosed in JP-A-58-190665. It can be divided into those that use fluctuations. By the way, in recent years, as one of superconducting devices, a superconducting quantum interference device (Superconductive Quantum Interference Dev.
Ice: hereinafter abbreviated as SQUID) is drawing attention.
By connecting a magnetic flux input circuit composed of a superconducting coil to this SQUID, a magnetometer capable of measuring an extremely weak magnetic flux such as a magnetic field accompanying a minute current flowing in a living body or a magnetic field from a minute magnet in the body is obtained. be able to.

However, when a gas pressure drive type GM refrigerator having the above-mentioned electric actuator is used to cool the SQUID to an operating temperature level, a magnetic flux is generated in the refrigerator, such as a motor or a solenoid valve. Since the actuator is provided, there is a disadvantage that the magnetic flux from the actuator is detected as harmful noise and the measurement accuracy is reduced.

Therefore, conventionally, in order to reduce the influence of the valve motor, the valve and the valve motor in the expander are separated from the cylinder portion, and the valve motor assembly and the cylinder assembly are connected by a pipe, so that the valve motor is SQUID, that is, a separate type is proposed in which the harmful noise due to the magnetic flux from the valve motor is reduced away from the tip of the cylinder (for example, the paper “Gifford-Mcmahon Refrigerator With” published in “NASA Conference Publication 2287”). Split Co
ld Head "and the paper" Development of A Hybrid Gifford-Mcmahon Jo "at the conference" 5th International Cryocooler Conference "held from August 18, 1988 to August 19, 1988.
ule-Thompson Based Neuromagnetometer, Cryosquid ”).

[0006]

However, in an integral type expander in which a valve motor is integrated with a cylinder portion, high and low pressure gas circulates between the compressor and the low temperature end (tip end) of the cylinder. ), The heat of compression taken by the gas is released while the gas returns to the compressor, so there is no problem, but in the separate expander as described above, the amount of refrigerant gas circulating between the compressor and Therefore, the heat of compression taken by the gas at the low temperature end (tip) of the cylinder is not sufficiently released, and accumulates in the room temperature portion (base end portion) of the cylinder. This heat retention heats the surge volume located at the base end of the cylinder, increasing the gas pressure inside it, reducing the differential pressure between the intermediate and high pressures of the gas, and smoothing the slack piston and displacer. There are disadvantages that the movement is hindered, the cooldown time becomes long, and the refrigerating capacity at the time of steady suspension after the cooldown decreases. Fig. 5 shows the P of the integrated expander and the separate expander.
An example of the V-line diagram is shown, and it can be seen that in the separate-type expander, the so-called PV illustrated capacity is reduced by the amount of pressure loss, and the refrigeration capacity is reduced. Of course, the load on the compressor also increases.

In order to solve the above-mentioned problems, it has been proposed to install a switching valve without an electric motor in an expander (see Japanese Patent Laid-Open No. 4-68266). The cryogenic refrigerator described in Japanese Unexamined Patent Publication No. 4-68266 has a valve motor installed at a position sufficiently separated from the expander, and has one of two pressure chambers for reciprocating the valve element of the switching valve. The pressure wave generated by the valve motor is supplied, and the discharge side and suction side of the compressor are connected to the other. Therefore, an intermediate pressure between the high pressure, which is the discharge side pressure of the compressor, and the low pressure, which is the suction side pressure, is always applied to the other pressure chamber, and the intermediate pressure and the pressure wave generated by the valve motor are The differential pressure causes the valve element to operate, allowing the expander to selectively communicate with the discharge side or the suction side of the compressor.

However, since the valve body is operated by the differential pressure between the pressure wave generated by the valve motor and the intermediate pressure, the operating pressure of the valve body cannot be increased sufficiently, and as a result, the valve body is operated. Of the valve body becomes slow and the time required from the start of the operation of the valve element to the completion of the operation becomes long. Further, if the seal between the other pressure chamber and the high-pressure side pipe is incomplete, the intermediate pressure will be high, so the movement of the valve body will be remarkable when a high-pressure pressure wave is supplied to the one pressure chamber. If the seal resistance becomes large and the seal resistance is large, the valve body cannot be operated.

[0009]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems, and can make the operation of the switching valve quick and smooth, and thus delay the switching of the gas pressure in the expansion space and cause blunting. It is an object of the present invention to provide a cryogenic refrigerator capable of preventing the above.

[0010]

A cryogenic refrigerator according to claim 1 is a compressor for compressing a refrigerant gas to generate a high pressure gas, and a high temperature gas supplied from the compressor for adiabatic expansion to achieve a cryogenic level. Is a cryogenic refrigerator configured with an expander for generating cold, the expander reciprocating the displacer by supplying and exhausting gas into and from the cylinder through the gas supply and exhaust port, It consists of a cylinder assembly that expands gas in the expansion chamber, a switching valve that selectively connects the gas supply / discharge port to the discharge side or suction side of the compressor, and a valve motor that generates a pressure wave that drives the switching valve. The switching valve has two pressure chambers for reciprocating the valve body, and a pressure chamber for operating the valve body to communicate the gas supply / discharge port with the discharge side of the compressor. Valve motor pressure wave Communicates with the raw part, a pressure chamber for operating the valve body to pass communication between the suction side of the compressor gas supply and discharge port is in communication expansion space and the communication of the expander.

A cryogenic refrigerator according to a second aspect is provided with a small diameter portion which functions as a resistance against a gas flow at a predetermined position of a gas flow path connecting an expansion space of the expander and a switching valve. is there.

[0012]

According to the cryogenic refrigerator of claim 1, the expansion space of the expander has a low pressure, and the pressure chamber for operating the valve body to connect the gas supply / discharge port and the discharge side of the compressor ( In the state in which the pressure of one pressure chamber is also low, the pressure chamber for operating the valve body to connect the gas supply / discharge port and the suction side of the compressor (hereinafter, the other pressure chamber). If a pressure wave (high pressure wave) of the valve motor is supplied to the valve motor, the valve body moves to one pressure chamber side due to the pressure difference between the pressure chambers, and the high pressure gas discharged from the compressor expands. Can be supplied inside the machine.

On the contrary, when the high-pressure gas discharged from the compressor is supplied to the inside of the expander, the expansion space of the expander has a high pressure, and one pressure chamber has a high pressure, the other pressure chamber has a valve. When the pressure wave (low-pressure pressure wave) of the motor is supplied, the valve body moves to the other pressure chamber side due to the pressure difference between the two pressure chambers, and the gas inside the expander flows into the suction side of the compressor.

In any case, the pressure in one pressure chamber changes following the pressure change in the expansion space of the expander, and the pressures in both pressure chambers eventually become equal. Therefore, by cyclically changing the pressure wave of the valve motor to a high pressure and a low pressure, the expansion space of the expander can be communicated with the discharge side and the suction side of the compressor periodically and alternately. The gas pressure in the expansion space of the machine is changed to a high pressure or a low pressure, and the displacer reciprocates accordingly, and the refrigeration cycle can be performed in the same manner as a normal refrigerator.

Further, in this cryogenic refrigerator, as the pressure for operating the switching valve, only the high pressure and the low pressure are adopted without adopting the intermediate pressure, so that the valve body of the switching valve is The pressure difference for operating the valve element can be made sufficiently large, and as a result, the valve element can be operated quickly and smoothly, which in turn delays the switching of the gas pressure in the expansion space and causes blunting. Occurrence can be prevented.

According to the cryogenic refrigerator of claim 2, a small diameter portion functioning as a resistance to the gas flow is provided at a predetermined position of the gas flow path connecting the expansion space of the expander and the switching valve. Since it is adopted, it is possible to prevent a sudden pressure change in the pressure chamber connected to the expansion space of the expander, and it is possible to greatly suppress heat generation due to the pressure change, and to switch the switching valve. It is possible to eliminate the need for special equipment for cooling the.

[0017]

Embodiments will be described in detail below with reference to the accompanying drawings showing embodiments. FIG. 1 is a vertical cross-sectional view showing the entire structure of a gas pressure drive type GM type cryogenic refrigerator as one embodiment of the present invention, and FIG. 2 is an enlarged vertical cross-sectional view showing the structure of a switching valve. This refrigerator is used as a pre-cooling refrigerator for a JT refrigerator utilizing Joule-Thomson expansion of helium gas (refrigerant gas), and this JT refrigerator cools an SQUID (not shown) to a cryogenic level. Has become. In FIG. 1, 1 is a compressor that compresses helium gas as a refrigerant gas to generate high-pressure gas, and 2 is an expansion that adiabatically expands the high-pressure gas supplied from the compressor 1 to generate cryogenic cold. It is a machine. The expander 2 is composed of the cylinder assembly 3, the switching valve 63, and the valve motor assembly 40.

The cylinder assembly 3 has a cylinder 10 having a bottomed cylindrical shape that is opened upward, and a valve stem 4 that hermetically closes an opening on the upper end side (base end side) of the cylinder 10. The valve stem 4 has, in the cylinder 10, a columnar protrusion 4a that protrudes concentrically from the inner wall of the cylinder 10 with a predetermined gap. Also, the valve stem 4 has
Gas supply / discharge port 5 opening on the cylinder center line on the upper surface
And a surge volume 7 having a relatively small capacity, and a gas flow path 8 that connects the gas supply / discharge port 5 to the inside of the cylinder 10. Further, the gas flow passage 8 is always in communication with the surge volume 7 via a communication passage 9 having a small passage cross-sectional area, and the communication passage 9 sets the intermediate pressure in the surge volume 7 to an appropriate value.

The cylinder 10 is formed in a two-stage structure with a large diameter portion 10a on the upper end side (base end side) and a small diameter portion 10b continuous to the lower end (tip) of the large diameter portion 10a. 1
At the lower end of 0a is a first-stage heat station 11 which is maintained at a temperature level of 55 to 60K, and at the lower end of the small diameter portion 10b is at a lower temperature level of, for example, 15 to 20K than the first-stage heat station 11. The second stage heat station 12 is provided for holding the helium gas in the JT refrigerator (not shown) to be pre-cooled.

Inside the upper end of the large diameter portion 10a of the cylinder 10, a slack piston 15 for partitioning and forming the intermediate pressure chamber 13 is arranged inside the large diameter portion 10a, and the intermediate pressure chamber 13 is a surge volume inside the valve stem 4. 7 through the orifice 14 at all times. The slack piston 15 is of a substantially cup shape having a bottom wall, and the upper end of the inner circumference is the outer circumference of the protruding portion 4a of the valve stem 4, and the lower end of the outer circumference is the cylinder 1.
The inner diameter of the large diameter portion 10a of 0 is slidably contacted with each other. Further, a center hole 15a is formed at the center of the bottom wall of the slack piston 15, and a plurality of communication holes 15b, 15b, ... Which communicate the inside and outside of the piston 15 are formed at the corners of the bottom wall.

A displacer 16 is reciprocally fitted in the cylinder 10. The displacer 16 is continuous with a large-diameter portion 16a which is arranged so as to be airtightly slidable in the large-diameter portion 10a of the cylinder 10 and a lower end (tip) of the large-diameter portion 16a, and is airtight with the small-diameter portion 10b of the cylinder 10. It has a two-stage structure composed of a slidably arranged small-diameter portion 16b, and a sealed space is formed inside each of the large-diameter portion 16a and the small-diameter portion 16b. The space is surrounded by the gas supply / discharge chamber 17 surrounded by the upper end of the displacer 16 and the slack piston 15, the large diameter portion 16a of the displacer 16 and the large diameter portion 10a of the cylinder 10, and corresponds to the first-stage heat station 11. The second-stage heat station is surrounded by the first-stage expansion chamber 18, the small-diameter portion 16b of the displacer 16 and the small-diameter portion 10b of the cylinder 10. Is partitioned into a second stage expansion chamber 19 that corresponds to 2. ． Further, at the lower end of the large-diameter portion 16a of the displacer 16, there are formed communication holes 20, 20 for constantly communicating the closed space inside the large-diameter portion 16a with the first-stage expansion chamber 18. In addition, a space within the small diameter portion 16b is provided at the upper end of the small diameter portion 16b.
Communication holes 21 and 21 which always communicate with the stage expansion chamber 18 are formed, and communication holes 22 and 22 which constantly communicate the closed space with the second stage expansion chamber 19 are formed at the lower ends thereof.

Further, at the upper end of the large diameter portion 16a of the displacer 16, a tubular locking piece 23 for communicating the space inside the large diameter portion 16a with the gas supply / discharge chamber 17 is integrally provided, and the locking piece 23 is provided. Is the central hole 15 in the bottom wall of the slack piston 15
A flange-shaped engaging portion 23a that engages with the bottom wall of the piston 15 is integrally formed at the upper end of the slack piston 15 when the slack piston 15 moves upward. When the piston 15 is lifted by a predetermined stroke, the displacer 16 is driven by the piston 15 to start rising by engagement of the bottom wall of the piston 15 with the locking portion 23a of the locking piece 23, that is, the displacer 16 is moved by a predetermined stroke. With a delay of 15
It is designed to move following.

A first-stage regenerator 24 (regenerator) is placed in the closed space inside the large-diameter portion 16a of the displacer 16, and a second-stage regenerator 25 is placed in the closed space inside the small-diameter portion 16b. It has been inserted. Each of these regenerators 24 and 25 is composed of a cold storage type heat exchanger. Specifically, the first stage regenerator 24
Is a stack of a large number of disk-shaped copper meshes as a cold storage material in a closed space, while the second stage regenerator 25 has a large number of lead balls (lead Shot) is filled and enclosed, and the mesh of these meshes and the gap between the lead balls serve as a gas passage. The cold heat of the helium gas flowing through this gas passage is stored in the mesh and each lead ball. That is, when the displacer 16 is in the intake stroke in which it rises in the cylinder 10, the mesh and lead balls that have dropped to the cryogenic temperature level in the previous exhaust stroke are transferred from the gas supply / discharge chamber 17 to the first and second expansion chambers 18, 19. It is brought into contact with the helium gas at room temperature, and the heat exchange between the two cools the gas to near the cryogenic level. On the other hand, when the displacer 16 is in the descending exhaust stroke, the helium gas whose temperature has dropped to an extremely low temperature level due to expansion in the expansion chambers 18 and 19 is brought into contact with the mesh and the lead ball while being discharged to the outside of the cylinder 10, It is configured to re-cool the mesh and the lead ball to near the cryogenic level by the heat exchange of.

As shown in FIG. 2, the switching valve 63 has a cylindrical casing 63a in which a valve element 63b is slidably housed in a reciprocating manner, and first and second valve elements 63b are provided on both sides of the valve element 63b. Two pressure chambers 63c and 63d are formed. Further, in a state of penetrating a predetermined position of the casing 63a, first and second pipe lines 63e and 63f which are respectively communicated with the discharge side and the suction side of the compressor 1 are provided, and the gas supply of the cylinder assembly 3 is performed. A third conduit 63g communicating with the outlet 5 is provided. The valve body 63b has a recess 63h for communicating the third conduit 63g with the first conduit 63e or the second conduit 63f on the outer periphery of the central portion, and the recess 63h and both pressure chambers. It has a seal member 63i for maintaining airtightness between 63c and 63d.
Further, a second pressure chamber 63d (a pressure chamber on the right side in FIG. 1) for operating the valve body 63b so that the third pipe passage 63g communicates with the second pipe passage 63f that communicates with the suction side of the compressor 1. Through the fifth pipe 63k and the middle of the third pipe 63g. Then, the first pressure chamber 63c (the left pressure chamber in FIG. 1) for operating the valve body 63b so that the third pipe 63g communicates with the first pipe 63e that communicates with the discharge side of the compressor 1. Is communicated with the pressure wave output port (gas supply / discharge port) 45 of the valve motor 54 via the fourth pipe 63j. Further, at a predetermined position of the fifth pipe 63k, a small diameter portion (for example, a needle valve) that functions as a resistance against the gas flow.
63m is provided.

The valve motor assembly 40 including the valve motor 54 is a hermetically sealed structure including a cylindrical valve housing 41 having a closed upper end and a valve stem 42 that hermetically closes the lower opening of the housing 41. It is cylindrical and has a high pressure gas inlet 43 connected to the discharge side of the compressor 1 and a low pressure gas outlet 44 connected to the suction side of the side wall of the valve housing 41. A gas supply / discharge port 45 having the same diameter as the gas supply / discharge port 5 of the cylinder assembly 3 is opened at the lower end of the valve stem 42. Inside the valve housing 41, a valve chamber 46 communicating with the high pressure gas inlet 43 is formed, and the valve chamber 46 faces the upper surface of the valve stem 42.

The valve stem 42 has a first gas passage 48 whose upper half is branched into two and communicates the valve chamber 46 with the gas supply / discharge port 45, and one end of which is described later in the first gas passage 48. A second gas flow path 49, which communicates with the low pressure port 53 of the valve disc 51 and has the other end communicating with the low pressure gas outlet 44 through a communication passage 50 formed in the valve housing 41, is formed. . Both gas channels 48,
As shown in FIG. 3, the reference numeral 49 designates a valve chamber 46 on the upper surface of the valve stem 42, a central portion of the valve stem 42 in the second gas passage 49, and two branch portions of the first gas passage 48. In that case, the second gas flow paths 49 are opened at symmetrical positions with respect to the openings.

Further, in the valve chamber 46, the valve motor 5
4 is provided with a valve disc 51 as a switching valve which is rotationally driven at a predetermined cycle.
By this switching operation, the valve chamber 46 communicating with the high pressure gas inlet 43 and the communication passage 50 communicating with the low pressure gas outlet 44 are alternately communicated with the gas supply / discharge port 45.

More specifically, the valve disc 51 is slidably connected to the output shaft 54a of the valve motor 54. A spring 55 is compressed between the upper surface of the valve disk 51 and the motor 54. The spring force of the spring 55 and the pressure of the high pressure helium gas introduced into the valve chamber 46 cause the lower surface of the valve disk 51 to move toward the valve stem. 42 is pressed against the upper surface with a constant pressing force. Further, as shown in FIG. 4, a pair of high pressure ports 52, 52 are formed on the lower surface of the valve disc 51 by cutting a predetermined length in the center direction from the outer peripheral edges facing each other in the radial direction.
And a low pressure port which is arranged at an angular interval of approximately 90 ° with respect to the high pressure ports 52, 52 in the rotational direction of the valve disc 51 and which is cut out in the diameter direction from the center of the lower surface of the valve disc 51 toward the outer peripheral edge. And 53 are formed. When the valve disk 51 is rotated by the drive of the valve motor 54 while pressing its lower surface against the upper surface of the valve stem 42 to perform a switching operation, the high pressure gas inlet 43 or the low pressure gas outlet 44 is operated in accordance with the switching operation of the valve disk 51. Are alternately communicated with the gas supply / discharge port 45 at a predetermined timing.

Then, by switching the valve disk 51 in the valve motor assembly 40, the high pressure gas from the high pressure gas inlet 43 or the low pressure gas from the low pressure gas outlet 44 is alternately acted on the gas supply / discharge port 5 of the cylinder assembly 3. Slack piston 15 and displacer 1
6 is reciprocated in the cylinder 10, and as shown in FIG. 3A, the high pressure ports 52, 52 on the lower surface of the valve disc 51 are
Of the high pressure port 5 when the inner ends of the valve chamber 46 and the first gas flow passage 48 on the upper surface of the valve stem 42 respectively match.
2, 52, the first gas flow path 48 and the refrigerant pipe 60 (or 61) to communicate with the gas supply / discharge chamber 17, the first and second stage expansion chambers 18 and 19 in the cylinder 10, and these chambers. By introducing and filling high-pressure helium gas into 17 to 19, the slack piston 15 and this piston 15
Raise the displacer 16 driven by.

On the other hand, as shown in FIG. 3 (B), the outer end of the low-pressure port 53, which is in constant communication with the second gas passage 49 opening on the upper surface of the valve stem 42 at the central portion, is the first gas passage 48.
If the chambers 17 to 19 in the cylinder 10
The refrigerant pipe 60 (or 61) and the first gas flow paths 48, 4
8, low pressure port 53, second gas passage 49 and communication passage 5
0 to communicate with the low pressure gas outlet 44, and each chamber 17 to
The helium gas filled in 19 is supplied to the low pressure gas outlet 44
The slack piston 15 and the displacer 16 are lowered by discharging them to the displacer 16
The helium gas in the expansion chambers 18 and 19 is expanded by the downward movement of the heat stations 11 and 12 to generate cold in the heat stations 11 and 12.

The operation of the cryogenic refrigerator having the above structure is as follows. At the time of cool down, the SQUID is gradually cooled to a low temperature level as the GM refrigerator and the JT refrigerator are operated, and the temperature of the SQUID is kept at an extremely low temperature level (about 4 ° C).
After descending to K), the refrigerator shifts to a steady operation state, and the SQUID operates in that state.

The operation of the GM refrigerator will be described in detail.
Cylinder 1 in cylinder assembly 3 of expander 2
When the pressure in 0 is low and the slack piston 15 and the displacer 16 are at the lower end position, the valve disk 54 is rotated by the drive of the valve motor 54 of the valve motor assembly 40, as shown in FIG. As shown, the high pressure ports 52, 52 coincide with the first gas passages 48, 48 on the upper surface of the valve stem 42 to open the valve disc 51 to the high pressure side. Accordingly, the high-pressure helium gas at room temperature supplied from the compressor 1 to the valve chamber 46 of the valve motor assembly 40 via the high-pressure gas inlet 43 is supplied to the high-pressure ports 52 and 52 of the valve disk 51 and the first gas flow. The gas is supplied to the gas supply / discharge port 45 via the passage 48, and is introduced from the gas supply / discharge port 45 to the first pressure chamber 54c of the switching valve 51 via the pipe line 54j. At this time, since the pressure inside the cylinder 10 is low, the pressure in the second pressure chamber 63d of the switching valve 63 is low. Therefore, the valve body 63b operates quickly and smoothly due to the pressure difference between the pressure chambers 63c and 63d, and the third pipe line 63g communicating with the gas supply / discharge port 5 is communicated with the discharge side of the compressor 1. It communicates with 1 conduit 63e. In this state, the gas is introduced into the gas supply / discharge chamber 17 below the slack piston 15 from the first pipe 63e through the switching valve 63, the third pipe 63g, the gas supply / discharge port 5 of the cylinder assembly 3 and the gas flow passage 8. It Further, this gas is supplied from the gas supply / discharge chamber 17 to the displacer 1
6 through the regenerators 24 and 25, respectively, and filled in the expansion chambers 18 and 19 in order.
While passing through 5, it is cooled by heat exchange with the copper mesh and lead spheres that were cooled in the previous exhaust stroke.

Further, since the intermediate pressure chamber 13 on the upper side of the slack piston 15 communicates with the surge volume 7 through the orifice 14, its pressure is kept at a constant proper value. Therefore, when high-pressure helium gas is introduced into the gas supply / discharge chamber 17, the internal pressure thereof becomes higher than that of the intermediate pressure chamber 13, and the piston 15 rises due to the pressure difference between the chambers 13 and 17. Then, when the piston 15 moves upward by a predetermined stroke, the bottom wall of the piston 15 and the locking piece 23 at the upper end of the displacer 16 are engaged with each other, and the displacer 16 is delayed with respect to the pressure change.
By the upward movement of the displacer 16, the expansion chambers 18 and 19 below the displacer 16 are further filled with high-pressure gas (intake stroke).

The displacer 16 includes the valve disc 5
Before 1 rotates 90 ° and closes, the ascending motion is almost completed and the upper end is reached. And the displacer 16
The valve disc 51 reaches 90 °
As shown in FIG. 3 (B), the low-pressure port 53 matches the first gas flow path 48 and the valve disc 51 opens toward the low-pressure side. As a result of this opening, the first pressure of the switching valve 63 is increased. The pressure in the chamber 63c becomes low. However, at this point in time, the pressure in the cylinder 10 is high, so the pressure in the second pressure chamber 63d is also high, and both the pressure chambers 63c, 63d.
The differential pressure causes the valve element 63b to quickly and smoothly move to the opposite side, thereby connecting the third conduit 63g and the second conduit 63f. Along with this communication, the helium gas in the expansion chambers 18 and 19 below the displacer 16 expands by Simon, and the expansion of the helium gas produces cold (expansion stroke).

The helium gas in this cryogenic state is
Contrary to the above-described gas introduction, the gas flows through the regenerators 24 and 25 in the displacer 16 and returns into the gas supply / discharge chamber 17, while cooling the copper mesh and the lead balls in the regenerators 24 and 25 at room temperature. Can be warmed up to. The helium gas at room temperature is, together with the gas in the gas supply / discharge chamber 17, the gas flow path 8, the gas supply / discharge port 5, the third pipe line 63g, the switching valve 63, the second pipe line, contrary to the above. 63f
Is sucked into the compressor 1 via. After the gas pressure decreases and becomes lower than the intermediate pressure chamber 13, the slack piston 15 descends due to the pressure difference between the chambers 13 and 17, and the bottom wall of the piston 15 contacts the upper surface of the displacer 16. The displacer 16 is pressed and descends, and the downward movement of the displacer 16 further discharges the gas in the expansion chambers 18 and 19 to the outside of the expander 2 (exhaust stroke).

Next, when the valve disc 51 is rotated 90 ° and closed, the displacer 16 descends to the lower end position. With the above, one cycle of the operation of the expander 2 is completed, and thereafter, the same operation as described above is repeated. By repeating this, the two-stage heat stations 11 and 12 of the cylinder 10 are gradually cooled, and the helium gas of the JT refrigerator that has received the cold from the two-stage heat stations 11 and 12 is pre-cooled. Cooled to low temperature level.

In order to operate the switching valve 63, the pressure in the second pressure chamber changes from low pressure to high pressure or from high pressure to low pressure. A small diameter portion 63m is provided in the middle of the fifth pipe 63k. Therefore, the pressure change can be performed slowly, and the temperature rise of the second pressure chamber 63d due to the pressure change can be suppressed. As a result, it is not necessary to provide a special cooling device. However,
When it is permitted to provide a cooling device, the small diameter portion 6
3m can be omitted.

As is apparent from the above description, the pressure difference for operating the valve element 63b of the switching valve 63 is not obtained by the pressure wave from the valve motor 54 and the intermediate pressure, but by the valve motor 54. Pressure wave and expander 2
Since it is obtained by the pressure of the expansion space of
A sufficiently large pressure difference can be obtained, the valve body 63b can be operated quickly and smoothly, and it is possible to prevent the inconvenience of delaying switching of the gas pressure in the expansion space and causing blunting. .

Further, when the switching valve 63 is not sufficiently sealed, the pressure in the high-pressure side pressure chamber will drop slightly or the pressure in the low-pressure side pressure chamber will rise slightly, but the valve body will be referenced to the intermediate pressure. Since the pressure difference for operating the valve element is obtained based on the high pressure and the low pressure, not the pressure difference for operating the valve element 63b. Therefore, the valve element 63b can be operated quickly and smoothly. Can be made.

[0040]

According to the first aspect of the present invention, a pressure difference for operating the valve body of the switching valve is obtained by the pressure wave generated by the valve motor and the expansion space pressure of the expander. The pressure difference can be increased as compared with the case where the pressure difference is obtained, and the valve element can be operated quickly and smoothly, which in turn delays the switching of the gas pressure in the expansion space and causes rounding. The unique effect of preventing the occurrence of is produced. Further, since the intermediate pressure is kept constant, the displacer moves stably and the refrigerating capacity also stabilizes.

According to the invention of claim 2, in addition to the effect of claim 1, there is a peculiar effect that the temperature rise in the switching valve can be suppressed.

[Brief description of drawings]

FIG. 1 is a gas pressure drive type G according to an embodiment of the present invention.
It is a longitudinal cross-sectional view which shows the whole structure of the cooldown operation state of M type cryogenic refrigerator.

FIG. 2 is an enlarged vertical sectional view of a switching valve.

FIG. 3 is a plan view of an upper surface of a valve stem facing a valve chamber.

FIG. 4 is a plan view of the lower surface of the valve disc.

FIG. 5 is a PV diagram of an integral type expander and a separate type expander.

[Explanation of symbols]

1 Compressor 2 Expander 3 Cylinder assembly 5 Gas supply / discharge port 10 Cylinder 16 Displacer 18, 19 Expansion chamber 45 Gas supply / discharge port 54 Valve motor 63 Switching valve 63b Valve body 63c 1st pressure chamber 63d 2nd pressure chamber 63k 5th Pipe line 63m small diameter part

Claims (2)

[Claims] 1. A compressor (1) for compressing a refrigerant gas to generate a high-pressure gas, and an expander (a) for adiabatically expanding the high-pressure gas supplied from the compressor (1) to generate cryogenic level cold. And a displacer (16) in which the expander (2) supplies and discharges gas into and from the cylinder (10) through the gas supply and discharge port (5).
Reciprocatingly moving the expansion chamber (18, 1) in the cylinder (10).
Cylinder assembly (3) for expanding gas in 9)
A switching valve (63) for selectively connecting the gas supply / discharge port (5) to the discharge side or the suction side of the compressor (1), and a valve motor (a motor generating a pressure wave for driving the switching valve (63)). 54), the switching valve (63) has two pressure chambers (63c) (63d) for reciprocating the valve body (63b), and the gas supply / discharge port (5). The pressure chamber (63c) for operating the valve body (63b) so as to establish communication between the compressor and the discharge side of the compressor (1) is communicated with the pressure wave generation section (45) of the valve motor (54), and gas supply / discharge is performed. Mouth (5) and compressor (1)
The pressure chamber (63d) for operating the valve body (63b) to communicate with the suction side of the expansion space (5) of the expander (2).
A cryogenic refrigerator characterized by being communicated with. 2. A small diameter portion (63) functioning as a resistance to a gas flow, at a predetermined position of a gas flow path (63k) connecting an expansion space of the expander (2) and a switching valve (63).
The cryogenic refrigerator according to claim 1, wherein m) is provided.